Rechargeable ZnMn Flat Plate Electrode Cell

ABSTRACT

Provided is a flat plate electrode cell, comprises positive electrode plates and negative electrode plates. The positive electrode plates each comprise manganese and compressed metal foam. The negative electrode plates each comprise zinc and compressed metal foam. Both the positive and negative electrodes can have alignment tabs, wherein the flat plate electrode cell can further comprise electrical terminals tanned from the aligned tabs. The rechargeable flat plate electrode cell of the present disclosure, formed from compressed metal foam, provides both low resistance and high rate performance to the electrodes and the cell. Examples of improvements over round bobbin and flat plate cells are current density, memory effect, shelf life, charge retention, and voltage level of discharge curve. In particular, the rechargeable flat plate electrode cell of the present disclosure provides longer cycle life with reduced capacity fade as compared with known round bobbin and flat plate cells.

This application is a continuation of application Ser. No. 13/120,441,filed Mar. 23, 2011, which claims priority under 35 USC 1.119(e) to U.S.Provisional Application No. 61/100,318 filed on Sep. 26, 2008, all ofthe foregoing being hereby incorporated in their entirety by reference.

BACKGROUND

Currently, the only batteries (rechargeable or non-rechargeable)commercially available with ZnMn chemistries are round bobbin cells.ZnMn chemistries are low cost and lightweight, are environmentallybenign, and have a very long charge retention. Round bobbin cells have apositive electrode that is stamped or pressed into a cylindrical hollowpellet and seated into a can, and the negative electrode is a gel thatis filled into the center void of the positive electrode.

The high internal resistance of low capacity round bobbin cells limitsthe currents (i.e., power) that they can deliver. In contrast, flatplate (electrode) cells can be scaled up to large sizes providing highcurrents and storage capacities.

CA 2 389 907 A1 relates to a method of producing flat plate electrodesin a small format that exhibit high current densities, higherutilization of the active materials, and better rechargeability. Themethod of forming the electrodes requires the active materials, binders,thickening agents, additives, and an alkaline electrolyte to form apaste that is applied to a current collector. CA 2 389 907 A1 providesis a flat plate rechargeable alkaline manganese dioxide-zinc cell.

What is needed are low cost, lightweight, environmentally friendlybatteries that can be used, for example, for large power back-upsystems, which are primarily currently served by lead acid and NiCdchemistries. Such batteries should exhibit improvements in, for example,current density, memory effect (i.e., capacity fade), shelf life, chargeretention (e.g., at higher operation temperatures), and voltage level ofdischarge curve over known round bobbin and flat plate cells.

SUMMARY

Provided is a flat plate electrode cell. The flat plate electrode cellcomprises positive electrode plates and negative electrode plates. Thepositive electrode plates each comprise manganese and compressed metalfoam. The negative electrode plates each comprise zinc and compressedmetal foam. The positive electrode plates can have aligned tabs and thenegative electrode plates can have aligned tabs, and the flat plateelectrode cell can further comprise a positive terminal formed from thealigned tabs of the positive electrode plates and a negative terminalformed from the aligned tabs of the negative electrode plates.

The rechargeable flat plate electrode cell of the present disclosureprovides improvements in, for example, current density, memory effect(i.e., capacity fade), shelf life, charge retention (e.g., at higheroperation temperatures), and voltage level of discharge curve over knownround bobbin and flat plate cells. In particular, the rechargeable flatplate electrode cell of the present disclosure provides longer cyclelife with reduced capacity fade as compared with known round bobbin andflat plate cells.

The rechargeable flat plate electrode cell of the present disclosureachieves such benefits primarily through unique electrode formation. Inparticular, both the positive and negative electrode of the rechargeableflat plate electrode cell of the present disclosure are formed fromcompressed metal foam, which provides both low resistance and high rateperformance to the electrodes and the cell.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWING

FIG. 1 depicts an embodiment of the assembly of positive (cathode)electrode plates and negative (negative) electrode plates.

FIG. 2 shows the improvements of the rechargeable flat plate electrodecell of the present disclosure over commercially available ZnMn roundbobbin consumer cells in terms of Cell Capacity Versus Discharge Rate.

FIG. 3 shows the improvements of the rechargeable flat plate electrodecell of the present disclosure over commercially available ZnMn roundbobbin consumer cells in terms of Cell Capacity versus Cycles/Life.

DETAILED DESCRIPTION

The rechargeable flat plate electrode cell of the present disclosurereduces the material costs, weight, toxicity (regulated limitations),volume, and maintenance of known batteries (e.g., batteries used forstationary power back-up applications), while increasing chargeretention and reliability. The rechargeable flat plate electrode cell ofthe present disclosure can be used wherever high capacity DC powerstorage is required, can replace lead acid or NiCd large formatbatteries or other high power electric back-up systems, and can be useddirectly in applications that can accept a wide voltage range and inconjunction with a voltage stabilizing system when the applicationrequires a narrower voltage range.

The rechargeable flat plate electrode cell of the present disclosurecomprises one or more anode plates comprising anode paste and one ormore cathode plates comprising cathode paste. The anode and cathodepastes each comprises active material metal powders (e.g., zinc andmanganese, respectively) mixed with aqueous or organic binder to createa paste that can be consistently coated on one or both sides of asubstrate. The substrate holds the active material (i.e., the paste) andacts as a current collector. In an embodiment, the substrate is made ofa conductive material such as steel, Ni, or Cu, and may be plated withindium or Ni (i.e., a material that is non-active relative to MnO₂) forthe cathode and Cu (i.e., a non-active material relative to zinc) forthe anode. In an embodiment, the substrate comprises a porous conductivesubstrate such as, for example, perforated metal, metal foam, metalfelt, expanded metal, or carbon foam. More specifically, the substratecomprises nickel foam and/or copper plated nickel foam. Accordingly, theanode or cathode paste is coated on and throughout the foam mesh.

The coated substrate is dried and sized (i.e., compressed) to create ahighly conductive, dense, porous flat plate electrode. The flat plateelectrodes are wrapped and sealed in a layer of barrier and separatormaterial to prevent short circuits and dendrite growth. The wrapped andsealed flat plate electrodes are stacked in an alternating cathode andanode pattern that is repeated until a desired capacity of the cell isreached. Tabs (collectors) of the flat plate cathode electrodes areconnected together and tabs of the flat plate anode electrodes areconnected together. In an embodiment, the rechargeable flat plateelectrode cell of the present disclosure is bi-polar. Such bipolarbatteries use a substrate to hold the positive active materials on oneside and negative active materials on the other and the substrate actsas a cell wall. The cell walls are sealed either peripherally ortangentially to hold internal pressure and electrolyte.

In metal foams, typically 75-95% of the volume consists of void spaces.As such, the use of metal foams allows for thicker electrode substrateswithout increasing the resistance of the electrode substrates. Targetcompression from sizing for this embodiment is between about 42% and45%, which gives desirable porosity, required for low resistance/highrate performance of the rechargeable flat plate electrode cell.

Without wishing to be bound by any theories, it is believed that thehigh density of compression reduces the resistance within the paste byreducing the distance between active particles in the active materialand reduces the resistance to the substrate by bringing the activeparticles closer to it. The high density reduces the volume so theenergy density is increased. The high density also reduces the voidvolume in the active material which reduces the amount of electrolyterequired to fill the electrode which in turn reduces the rate at whichdendrites are formed which protects the cell from shorting and increasescycle life. The density level is critical since over-compression willcause dry spots in the active material where electrolyte cannot get to.These dry spots are very high resistance which reduces performance andcan create gassing areas which cause cell failure.

Without sizing, desired energy density and high power capability are notachieved. The target coated sized thickness for the cathode is less thanabout 0.0300 inches. Coated sized thickness for the cathode greater thanabout 0.0300 inches results in rate capability (power) losses, whilecoated sized thickness for the cathode less than about 0.0200 inchesresults in energy density losses, due to excess inter electrode spacingand substrate relative to active material.

The anode paste comprises about 75-98 weight %, for example, about 83.1weight %, zinc active material; about 0.01-1.0 weight %, for example,about 0.27 weight %, polymeric binder; and about 0-20 weight %, forexample, about 16.6 weight %, solid zinc oxide. Exemplary zinc activematerials include lead-free zinc and zinc alloy, such as, for example,in metallic, powder, granular, particulate, fibrous, or flake form.

The cathode paste comprises about 70-90 weight % electrolytic manganesedioxide; about 2-15 weight %, for example, about 7.5 weight %, graphiteand/or carbon black; about 3-10 weight %, for example, about 6 weight %,polymeric binder; about 1-15 weight %, for example, about 5 weight %,barium compound; and about 0.01-10 weight %, for example, about 5 weight%, hydrogen recombination catalyst. Exemplary barium compounds includebarium oxide, barium hydroxide, and barium sulfate. Exemplary hydrogenrecombination catalysts include silver, silver oxides, and hydrogenabsorbing alloys. The cathode paste may further comprise indium.

Exemplary polymeric binders of either the cathode paste or anode pasteinclude carboxymethyl cellulose (CMC), polyacrylic acid, starch, starchderivatives, polyisobutylene, polytetrafluoroethylene, polyamide,polyethylene, and a metal stearate. The polymeric binder of either thecathode paste or anode paste can include conductive graphite, forexample, conductive graphite having an average particle size between 2and 6 microns.

The rechargeable flat plate electrode cell of the present disclosurediffers from currently commercially available rechargeable ZnMnbatteries in that the flat plate electrodes of the cell:

-   -   are flat;    -   have an internal carrier (substrate);    -   have a current collector attached to the internal carrier; and    -   have the anode's active material completely sealed in a barrier        to stop dendrite failures.

The rechargeable flat plate electrode cell of the present disclosurefurther differs from currently commercially available batteries in that:

-   -   flat plate cathode electrodes are produced by use of aqueous or        organic binder and metal powder which is coated, dried and        sized, instead of a glycol gel that is injected into a barrier        wrapped pocket, which allows for the production of high volume        flat plate electrodes required for economical power back-up        batteries;    -   flat plate anode electrodes are produced by use of an aqueous or        organic binder and metal powder which is coated, dried, and        sized, instead of mixing and then high pressure stamp forming        into a ridged pellet, which allows for the production of high        volume flat plate electrodes required for economical power        back-up batteries;    -   multiple flat plate cathode electrodes and flat plate anode        electrodes can be connected in parallel then placed in a        container, filled with electrolyte, and then sealed, instead of        a cathode pellet wedged into a metal can, a barrier separator        inserted into the cathode pellet cavity, and then anode gel        injected into the cavity with a metal pin inserted into the        center of the gel, and closed using a seal ring and crimping,        which allows for the high capacity required for stationary power        back-up batteries.

Advantages of the rechargeable flat plate electrode cell of the presentdisclosure include:

-   -   reducing battery cost through lower material costs, lower        production costs, and using fewer components;    -   reducing battery weight through higher energy dense chemistry,        and using fewer components;    -   reducing battery volume through higher energy dense chemistry,        and using fewer components;    -   reducing environmental and regulated (storage, disposal,        shipping) issues by using environmentally friendly chemistry;    -   improving reliability by using batteries with higher capacities        and internal series collectors so fewer batteries/connections        are used;    -   reducing continuous energy losses by using a chemistry with        higher charge retention; and    -   reduces energy losses in the system by improving performance        (charge efficiency, rate capability) through battery design that        reduces losses from internal resistance in the battery.

FIG. 1 depicts an embodiment of the assembly of positive (cathode)electrode plates and negative (anode) electrode plates. In particular,cathode plate C₁ is stacked atop anode plate A₁, which is stacked atopcathode plate C₂, which is stacked atop anode plate A₂. While not shownin FIG. 1, in the electrode stack, the alternating positive and negativeelectrode plates can be separated by separator layers, which insulatethe electrode plates from one another. Alternatively, the flat plateelectrodes can be wrapped and sealed in a layer of barrier and separatormaterial to prevent short circuits and dendrite growth, as explainedabove. The lightly shaded section of each of the electrode platesrepresents the portion thereof upon which cathode paste or anode paste,respectively, has been applied. The darkly shaded section of each of theelectrode plates represents the portion thereof which has been pressed(i.e., “coined”) to create a thin, flat, high density area (e.g., about0.15 inch wide), to which a tab can be welded. Accordingly, the unshadedsection of each of the electrode plates represents the tab (e.g., 1 inchwide) welded to the electrode plate. The tab can be, for example, copperor copper plated nickel. A positive terminal is formed from aligned tabsof the positive electrode plates and a negative terminal is formed fromaligned tabs of the negative electrode plates.

As illustrated in FIGS. 2 and 3, the rechargeable flat plate electrodecell of the present disclosure exhibits improved performance overcommercially available ZnMn round bobbin consumer cells. In particular,FIG. 2 shows the improvements of the rechargeable flat plate electrodecell of the present disclosure over commercially available ZnMn roundbobbin consumer cells (i.e., “Baseline Round Bobbin” and “Improved RoundBobbin”) as well as a cell as disclosed in CA 2 389 907 A1 in terms ofCell Capacity (expressed as a percentage of initial capacity) VersusDischarge Rate (expressed as a percentage of one hour capacity), whileFIG. 3 shows the improvements of the rechargeable flat plate electrodecell of the present disclosure over commercially available ZnMn roundbobbin consumer cells (i.e., “Baseline Round Bobbin” and “Improved RoundBobbin”) as well as a cell as disclosed in CA 2 389 907 A1 in terms ofCell Capacity (expressed as a percentage of initial capacity) versusCycles/Life (expressed as full charge/discharge at C/16 and RoomTemperature). As can be seen from FIG. 2, the rechargeable flat plateelectrode cell of the present disclosure has a capacity of greater than50% of initial capacity, and in particular, a capacity of greater than80% of initial capacity, at a discharge rate of greater than or equal to50% of one hour capacity. As can be seen from FIG. 3, the rechargeableflat plate electrode cell of the present disclosure has a capacity ofgreater than or equal to 60% of initial capacity at greater than orequal to 25 cycles at room temperature.

With further reference to FIG. 3, the Baseline Round Bobbin was testedfor seven cycles, the Improved Round Bobbin was tested for sixty-fivecycles, and a cell as disclosed in CA 2 389 907 A1 was tested for onehundred cycles. The rechargeable flat plate electrode cell of thepresent disclosure was tested for twenty-five cycles, with predictedresults shown for up to 200 cycles.

Additionally performance characteristics of the rechargeable flat plateelectrode cell of the present disclosure can include capacity of greaterthan 5 Ahr, cycle life exceeding 200 cycles at 80% DOD above 50% initialcapacity, power exceeding C/2 rate to 1 V at 50% initial capacity and 2Crate to 1V at 25% initial capacity, energy density exceeding 90 Whr/kg,and power density exceeding 180 W/kg. DOD, or depth of discharge, is ameasure of how much energy has been withdrawn from a battery, expressedas a percentage of full capacity. C/2 rate refers to a discharge rate of50% of one hour capacity.

The rechargeable flat plate electrode cell of the present disclosure canbe utilized in a vehicle for starting a internal combustion engine, orin a more portable format can be used in power tools, cell phones,computers, and portable electronic devices.

The following illustrative examples are intended to be non-limiting.

EXAMPLES

With regard to formation of the flat plate anode electrodes, 360 gramsof Zn, 72 grams of ZnO, and 59.88 grams of 2% CMC gel were mixed to forma paste comprising 83.1 weight % zinc active material (i.e., Zn), 16.6weight % solid zinc oxide, and 0.27 weight % polymeric binder. The pastewas applied to one side of copper plated nickel foam and pressed/workedin. The copper was plated on the nickel foam via copper plating 1A for30 minutes. Water was evaporated from the paste, and the dried pastedfoam was pressed to approximately 50% of its original thickness. A 0.15inch strip at the top of each flat plate anode electrode was coined forattachment of a tab. Further details of formed flat plate anodeelectrodes can be found in Table 1, below. With regard to the capacitycalculations in Table 1, the capacity of 0.625g Zn is 512 mAh.

With regard to formation of the flat plate cathode electrodes, 41.90grams of 2% CMC gel and 100 grams of cathode powder ground down to1/10^(th) of the initial particle size were mixed to form a paste. Thecathode powder comprised electrolytic manganese dioxide, 7.5 weight %graphite/carbon black, 5 weight % polymeric binding agent, 5 weight %barium compound, and 5 weight % hydrogen recombination catalyst, and ispressed to form high density initial particles. The 2% CMC gel providedan additional 1 weight % polymeric binding agent to provide a paste witha total of 6 weight % polymeric binding agent. The paste was applied toone side of nickel foam having a weight basis of 0.255 g/in². Water wasevaporated from the paste, and the dried pasted foam was pressed toapproximately 50% of its original thickness. A 0.15 inch strip at thetop of each flat plate cathode electrode was coined for attachment of atab. Further details of formed flat plate cathode electrodes can befound in Table 2, below.

TABLE 1 Anode Design Sized Thickness (Substrate Paste Sized Sized andPaste Weight/ Weight Width Length Weight Width Length Paste) Sized AreaSubstrate (g) (in) (in) (g) (in) (in) (in) (g/in²) A · h/in² A · h/in³ 12.669 2.52 2.37 13.098 2.54 2.50 0.0370 2.063 1.406 37.988 2 2.697 2.522.37 13.258 2.54 2.52 0.0370 2.071 1.411 38.147 3 2.634 2.53 2.38 15.0612.54 2.53 0.0380 2.344 1.597 42.027 4 2.679 2.52 2.35 13.833 2.53 2.470.0370 2.214 1.508 40.767 5 2.631 2.53 2.38 15.144 2.55 2.55 0.03802.329 1.587 41.763 6 2.699 2.50 2.39 14.534 2.53 2.50 0.0370 2.298 1.56642.319 7 2.375 2.54 2.36 15.238 2.56 2.49 0.0380 2.390 1.629 42.867 82.360 2.54 2.36 14.495 2.55 2.48 0.0370 2.292 1.562 42.212 9 2.339 2.522.38 15.492 2.55 2.48 0.0380 2.450 1.669 43.929 10 2.308 2.53 2.3816.602 2.55 2.50 0.0390 2.604 1.775 45.502 11 2.618 2.53 2.37 14.3802.54 2.51 0.0360 2.256 1.537 42.694

TABLE 2 Cathode Design Paste Sized Weight/ Sized Thickness Sized CoatedPaste Sized Sized Coated (Substrate Coated Weight Width Length ThicknessLength Weight Width Length Length and Paste) Area Substrate (g) (in)(in) (in) (in) (g) (in) (in) (in) (in) (g/in²) mAh/in² 1 1.168 2.53 1.810.058 1.54 4.492 2.57 2.02 1.77 0.0250 0.988 216 2 1.170 2.52 1.82 0.0541.56 4.129 2.57 1.97 1.72 0.0235 0.934 205 3 1.141 2.50 1.79 0.050 1.563.555 2.52 1.90 1.66 0.0225 0.850 186 4 1.149 2.49 1.81 0.049 1.57 3.5772.54 1.94 1.69 0.0230 0.833 182 5 1.143 2.49 1.80 0.048 1.58 3.756 2.541.94 1.72 0.0230 0.860 188 6 1.138 2.48 1.80 0.050 1.58 3.815 2.53 1.941.72 0.0235 0.877 192 7 1.139 2.51 1.78 0.052 1.55 4.328 2.56 1.96 1.750.0235 0.966 212 8 1.154 2.50 1.81 0.050 1.56 4.067 2.56 1.96 1.690.0235 0.940 206 9 1.152 2.51 1.80 0.050 1.58 4.041 2.56 1.94 1.740.0230 0.907 199

Many modifications of the exemplary embodiments disclosed herein willreadily occur to those of skill in the art. Accordingly, therechargeable flat plate electrode cell of the present disclosure is tobe construed as including all structure and methods that fall within thescope of the appended claims.

1. A flat plate electrode cell comprising: positive electrode plates each comprising: manganese containing compressed metal foam, the metal foam having a compression sizing between about 42 and 45%; and negative electrode plates each comprising: zinc containing compressed metal foam, the metal foam having a compression sizing between about 42 and 45%.
 2. The flat plate electrode cell of claim 1, wherein: the positive electrode plates have aligned tabs; and the negative electrode plates have aligned tabs; and the flat plate electrode cell further comprises: a positive terminal formed from the aligned tabs of the positive electrode plates; and a negative terminal formed from the aligned tabs of the negative electrode plates.
 3. The flat plate electrode cell of claim 1, wherein the negative electrode plate comprises an anode paste.
 4. The flat plate electrode cell of claim 3, wherein the anode paste comprises 75-98 weight % zinc active material.
 5. The flat plate electrode cell of claim 4, wherein the zinc active material comprises lead-free zinc or zinc alloy.
 6. The flat plate electrode cell of claim 1, wherein the positive electrode plate comprises a cathode paste.
 7. The flat plate electrode cell of claim 6, wherein the cathode paste comprises from about 70 to 90 weight % electrolytic manganese dioxide.
 8. The flat plate electrode cell of claim 6, wherein the cathode paste comprises from about 2 to 15 weight % of graphite and/or carbon black.
 9. The flat plate electrode cell of claim 1, wherein the manganese containing compressed metal foam and/or the zinc containing compressed metal foam further comprises carboxymethyl cellulose (CMC).
 10. The flat plate electrode cell of claim 9, wherein the CMC is present in the form of 2% CMC gel.
 11. The flat plate electrode cell of claim 9, wherein both the manganese containing compressed metal foam and the zinc containing compressed metal foam comprises CMC.
 12. The flat plate electrode cell of claim 9, wherein only the manganese containing compressed metal foam comprises CMC.
 13. The flat plate electrode cell of claim 9, wherein only the zinc containing compressed metal foam comprises CMC. 